Many products are manufactured from elongated sheet or stock material that is shipped and stored in the form of a roll or coil. Continuous strips or webs of thin, flexible material are commonly provided on storage rolls that are subsequently unwound for production of items made from these materials. Examples of these materials are plastic film, metal foil, tissue and paper.
During the manufacture of paper products such as napkins, newspapers, and magazines, for example, very large storage rolls of paper are used to provide the stock material from which the paper items are produced. The storage rolls are then unwound for further processing such as cutting, folding or printing.
Unwinding machines receive large rolls of sheet material wound on a tubular core and unwind the sheet material for processing. The rolls may have a length of up to about 300 inches (750 cm) and a weight of up to about 8,000 lbs (3600 kg). Processing on machines such as printing machines or laminating machines to which the sheet material is supplied by the unwinding machine usually require the sheet material to be supplied at a constant speed and tension. When nearly all the sheets on a roll have been unwound from the core, it is necessary for the machine to stop unwinding sheet from the almost empty roll and to commence unwinding sheet from a new roll without any interruption in the supply of sheets to the processing machine. It is thus necessary for the sheet to be cut from the nearly empty roll and to be secured to the sheet on the new roll to ensure a continuous supply of sheet.